Masters project on heat recovery in an aluminium plant

28.1.2019

EFLA engineer, Leó Blær
Haraldsson, just completed his MSc degree in mechanical engineering. His thesis
reports on an interesting project, which has attracted quite a bit of
attention. The project examines the possibility of utilizing the thermal energy
in exhaust gas from the Alcoa Fjarðaál aluminium plant to heat water for house
heating in the nearby community of Reyðarfjörður.

Leo Blær Haraldsson, Mechanical engineer at EFLA.

Leó‘s thesis is titled
"Viability of a district heating system in Fjarðabyggð using waste heat
from Alcoa Fjarðaál" and this thesis covers the basic design of a heat
recovery system and distribution system as well as cost estimate.

Aluminium is produced
at Alcoa Fjarðaál using a great deal of energy, which comes from an
already-built hydroelectric plant. About half of the energy used for aluminium
production escapes as heat. Instead of blowing this energy into the atmosphere
it could be harnessed for district heating in Reyðarfjörður. According to Leó
Blær, „the project findings indicate that heat recovery from the exhaust gases
at Fjarðaál is technically possible and will require connecting to only one
fourth of the total plant gas flow.“

Reduced fluoride emissions

Positioning of a heat
recovery system in an aluminium plant is important. The heat exchanger can be
installed in the gas flow before the gas travels through the gas treatment
center. At this point, the gas is 15°C warmer than after the gas treatment
center and, therefore, there is more heat that can be harnessed. Fluoride
binding in the gas treatment center increases with lower gas temperatures which
results in less fluoride emitting to the atmosphere. However, the gas is
dirtier before it goes through the gas treatment center and can form a dust
film inside the heat exchanger pipes. This can increase pressure drops and
reduce the heat transfer coefficient. But clever heat exchanger design can
minimize dust film formation.

Similar methods in Norway

Leó has studied
several successful heat recovery systems in aluminium plants. „For example, in
Mosjøen, Norway, there is a heat exchanger connected to the gas exhaust from
eight pots and the energy is used to heat the plant itself. This heat exchanger
is connected to the gas before it enters the gas treatment center. It has been
in use since 2009 and there has been no need to clean it due to dust film
buildup.“

There are also
examples where all the gas from an aluminium plant is sucked through a heat
exchanger to cool the gas before treating it in the gas treatment center. The
recovered heat is not used for any specific purpose. Rather, this is done
instead of blowing cold air or water mist into the gas flow to cool it. This
method increases gas volume and calls for more power to the main fans.

Alcoa Fjarðaál aluminium plant

Excess energy could be used for swimming facilities

Reyðafjörður is in one
of the few locations in Iceland where geothermal heat is not available for
heating and houses must be heated with electricity. This is considerably more
expensive than geothermal heating. The amount of power needed to heat houses
and for water for household use in Reyðarfjörður is estimated to be 5 MWth. The heat recovery system designed in
this project will supply 5,2 MWth. Thus,
there will be excess energy available, particularly during the warmer months of
the year. This energy could, for example, be used to heat new swimming
facilities in Reyðarfjörður or a warm water beach.

Benefits

The estimated cost for
a heat recovery system and distribution system is 2.5 billion ISK. The
Icelandic Government currently subsidizes distribution costs for electricity
for house heating in Reyðarfjörður and if the Government would provide seed
funding amounting to 12 years‘ worth of subsidies no loans would need to be
taken. This would be the same amount the Government would be paying in
subsidies over 12 years assuming continued heating using electricity. If the
project becomes a reality, the Government would no longer need to subsidize
distribution costs to Reyðarfjörður and the population would have access to
ample hot water at a price similar to what most people in Iceland pay.

Furthermore, Alcoa Fjarðaál can
expect social, environmental and even financial benefits from such a project.

Positive reactions to the project

Leó conducted his
research in collaboration with EFLA, and Gestur Valgarðsson, who leads the Mechanical
division was one of three thesis supervisors. EFLA presented the project on January
23rd at Fjarðaál and the local municipality. The presentation received positive
response from both groups and it will be very interesting to follow future
steps in this project.